Do not reinflate navbar on theme changes

ASSET_PATH events don't require reinflation of the navbar, we should use
onNavigationModeChanged instead to control which navbar style to draw.

Test: change wallpapers. observe navbar not being recreated
Test: change navigation mode
Test: change to guest, repeat tests
Fixes: 180976415
Change-Id: I2a8d1795f4849e69f3945f3b63be31375d3deddf